Re­si­li­ent al­gae may speed up Green­land ice melt

The tiny ice in­hab­it­ants darken the gla­cier sur­face and can thus ac­cel­er­ate its melt­ing.

Tiny algae darken the surface of glaciers and thus accelerate their melting. This is the case, for example, on the Greenland Ice Sheet, which plays an important role in our climate and is already melting increasingly fast due to global warming. A study by the Max Planck Institute for Marine Microbiology in Bremen, Germany, and the University of Aarhus, Denmark, now shows that the ice algae grow extremely efficiently, despite the fact that there are hardly any nutrients available to them on the ice.

Gla­ciers are huge white ice masses that can re­flect a lot of sun­light. However, es­pe­cially where the gla­ciers are not covered in snow and the bare ice is ex­posed, they some­times have dark patches. These are mi­cro­scopic al­gae that grow on the ice and darken its sur­face. As a res­ult of this dark­en­ing, the tiny in­hab­it­ants cause the ice to warm up and melt faster.

Mys­ter­i­ous al­gae growth

Little is known about where the small al­gae get the ne­ces­sary nu­tri­ents to sur­vive in this hos­tile en­vir­on­ment. A re­search team around Laura Hal­bach, Kath­ar­ina Kitzinger and Al­ex­an­dre An­esio from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy in Bre­men, Ger­many, and the Dan­ish Uni­versity of Aar­hus in­vest­ig­ated this ques­tion on the Green­land Ice Sheet. They dis­covered that the al­gae on the gla­cier ice are true cham­pi­ons of nu­tri­ent up­take. “I wanted to un­der­stand how such algal blooms can de­velop in Green­land,” ex­plains lead au­thor Laura Hal­bach from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy. Us­ing new meth­ods, Hal­bach was the first re­searcher ever to meas­ure how the al­gae ab­sorb and store nu­tri­ents. “The al­gae can grow and col­on­ize the ice des­pite the scarcity of nu­tri­ents,” says Hal­bach. “On the west coast of Green­land, around a tenth of the ice melt is already caused by these mi­cro­scopic in­hab­it­ants. In some cases, they darken the gla­cier sur­face so much that is even vis­ible on satel­lite im­ages. In view of the fact that the cli­mate is get­ting warmer and ever more snow-free areas and thus more po­ten­tial hab­itat for the al­gae ap­pears on the Green­land Ice Sheet, the al­gae’s abil­ity to ef­fi­ciently ab­sorb and store nu­tri­ents is par­tic­u­larly sig­ni­fic­ant.”

Ef­fi­cient nu­tri­ent up­take of global im­port­ance

The Green­land Ice Sheet plays an im­port­ant role in our cli­mate. Its melt­ing con­trib­utes sig­ni­fic­antly to global sea level rise, as it re­leases large quant­it­ies of fresh wa­ter into the oceans. Due to global warm­ing, the snow dis­ap­pears from ever more gla­cier areas and the ice is ex­posed. This cre­ates new areas that can be col­on­ized by ice al­gae, which in turn ac­cel­er­ates the melt­ing – a cycle that ur­gently needs to be un­der­stood in more de­tail. Here, the present study takes us a big step for­ward: “Un­til now, there have been no meas­ure­ments of how the ice al­gae sup­ply them­selves with nu­tri­ents,” says Hal­bach. “We are now clos­ing this gap with a par­tic­u­larly pre­cise method that al­lows us to meas­ure the nu­tri­ent up­take and stor­age of in­di­vidual cells. Our res­ults show that the al­gae can grow rap­idly even though there are hardly any nu­tri­ents avail­able on the spot. In­stead, they can ef­fi­ciently take up in­or­ganic ni­tro­gen and are good at stor­ing phos­phorus.”

If these ice al­gae are not oth­er­wise decim­ated, for ex­ample by para­sitic fungi or a lack of trace ele­ments, there would be little to stop their growth. They could grow on ex­posed ice sur­faces and thus in­tensify the ice melt – a po­ten­tial pos­it­ive feed­back with global warm­ing.

The find­ings of the re­search­ers led by Laura Hal­bach are not only fas­cin­at­ing, but also im­port­ant. They will help to bet­ter pre­dict the con­tri­bu­tion of the dark pig­men­ted al­gae to the melt­ing of the Green­land Ice Sheet. Cal­cu­la­tions of the an­nual ice melt are in­cor­por­ated into today’s cli­mate mod­els. The new find­ings could be used to im­prove the rep­res­ent­a­tion of the al­gae in mod­els pre­dict­ing the ice melt, and thus bet­ter in­cor­por­ate its ef­fect on the global cli­mate.

• Single-cell imaging reveals efficient nutrient uptake and growth of microalgae darkening the Greenland Ice Sheet. Nature Communications (on­line pu­bli­ca­ti­on Fe­bru­ary 19, 2025) – DOI: 10.1038/s41467-025-56664-6

Quelle

Max-Planck-Instituts für Marine Mikrobiologie 2025